Active matrix type organic electro luminescence display panel device and method of fabricating the same

ABSTRACT

An active matrix organic electro luminescence display panel device includes a substrate, at least one low refractive thin film formed on the substrate, and an organic electro luminescence diode formed on the low refractive thin film to selectively emit light. Also, a method of fabricating an active matrix organic electro luminescence display panel device includes the steps of forming at least one low refractive thin film on a substrate, and forming an organic electro luminescence diode on the low refractive thin film to selectively emit light.

The present invention claims the benefit of Korean Patent ApplicationNo. P2002-039475 filed in Korea on Jul. 8, 2002, which is herebyincorporated by reference. BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an organic electro luminescence(EL) display panel device and a method of fabricating the same, and moreparticularly to an active matrix type organic electro luminescencedisplay panel device and a method of fabricating the same havingextended life span and improved light emission efficiency.

[0003] 2. Discussion of the Related Art

[0004] In general, an organic EL display panel device is a passivematrix type or an active matrix type. A passive matrix type organic ELdisplay panel device does not include thin film transistors (TFTs)separately. In the passive matrix type organic EL display panel device,gate lines cross data lines to form a matrix and the gate lines aresequentially driven to drive each pixel of the device. However, aninstantaneous brightness is required to produce an average brightnessacross a number of lines to display images. Thus, if there are morelines in the device, higher voltage and current also required.Therefore, the passive matrix type organic EL display panel device haslimited resolution, power dissipation and life span.

[0005] In contrast, an active matrix type organic EL display paneldevice includes a thin film transistor located at each pixel functioningas a switch for opening and shutting each pixel. A voltage applied tothe pixel is charged to a storage capacitor and the charged voltage inthe storage capacitor acts to apply power source until the next framesignal is applied. Thus, the active matrix type organic EL display paneldevice is driven for one frame period regardless of the number of gatelines. Therefore, the active matrix type organic EL display panel devicehas better resolution, power dissipation and life span in comparison toa passive matrix type organic EL display panel device.

[0006]FIG. 1 is a diagram of a pixel structure of an active matrix typeorganic EL display panel device according to a related art. In FIG. 1,the basic pixel structure of the active matrix type organic EL displaypanel device includes a gate line GL formed in a first direction; apower supply line VDD and a data line DL formed in parallel in a seconddirection crossing the first direction at a predetermined interval; anda pixel area defined by the crossing of the gate line GL, the data lineDL and the power supply line VDD. In addition, the active matrix typeorganic EL display panel device includes a switching thin filmtransistor STFT connected to a storage capacitor Cst and the powersupply line VDD, and an organic EL diode OLED connected to a drive thinfilm transistor MTFT. The switching TFT STFT controls the drive of thedrive TFT MTFT in response to a selection signal from the gate line GL.

[0007] In the organic EL diode OLED, if an organic luminous material issupplied with a forward current, holes and electrons are moved to alight emission layer formed between a hole transport layer and anelectron transport layer through a hole injection layer, the holetransport layer, the electron transport layer and an electron injectionlayer that are deposited between an anode electrode supplying holes anda cathode electrode supplying electrons. The moved holes and electronsare combined together within the light emission layer to generate adesignated energy, which causes to emit light.

[0008] Further, if a signal is applied to a pertinent electrode inaccordance with the selection signal, the switching TFT STFT is turnedon. At this moment, a data signal is applied to the drive TFT MTFT andthe storage capacitor Cst through the switching TFT STFT. If the driveTFT MTFT is on, a current from the power supply line VDD is applied toan organic EL layer through the drive TFT MTFT. In this case, the openand close time of the drive TFT MTFT becomes different in accordancewith the size of the data signal, gray levels can be expressed by way ofcontrolling the amount of current flowing through the drive TFT MTFT.Thus, the organic EL display panel can emit light continuously until thesignal of the next frame is applied after a data charged in the storagecapacitor Cst is continuously applied to the drive TFT MTFT.

[0009] According to the driving principle, the active matrix typeorganic EL display panel can apply the voltage lower and the currentinstantaneously lower than the passive matrix type organic EL displaypanel, and the organic EL display panel can be continuously driven forone frame period regardless of the number of selected lines. Thus, theactive matrix type organic EL display panel is advantageous for lowpower dissipation, high resolution and a large screen. On the otherhand, the active matrix type organic EL display panel has a structurewhere a current flows through a TFT, a polycrystalline silicon p-Si TFTis required which has a uniform crystalline state so as for the electricfield effect mobility to be excellent because the related art amorphoussilicon a-Si TFT is difficult to be adopted because silicon particles ofnon-crystalline state of the amorphous silicon causes electric fieldeffect mobility to be low.

[0010] The polycrystalline silicon TFT has high electric field effectmobility, thus a drive circuit can be made on a substrate. Hereby, whenthe drive circuit is made on the substrate with the polycrystallinesilicon TFT, the cost and mounting of the drive integrated circuit ICcan be simplified. Polycrystalline silicon commonly is formed using alow temperature crystallization method including laser annealing ofamorphous silicon.

[0011]FIG. 2 is a sectional view of an active matrix type organic ELdisplay panel device according to the related art. In FIG. 2, theorganic EL display pane device includes an insulating substrate 1, abuffer layer 30 formed on an entire surface of the substrate 1, a thinfilm transistor T formed in a first region of the buffer layer 30, astorage capacitor Cst formed in a second region of the buffer layer 30,and an organic EL diode E formed in a light emission region I on thesubstrate 1. The thin film transistor T includes an active layer 32formed on the buffer layer 30, a gate electrode 38 formed on the activelayer 32, and source and drain electrodes 50 and 52 on the active layer32. The storage capacitor Cst includes a capacitor electrode 34 formedon the buffer layer 30 and a power electrode 42 formed opposite to thecapacitor electrode 34 with a first insulating layer 40 therebetween. Inaddition, the organic EL diode E includes an anode 58 formed on a thirdinsulating layer 54, and a cathode 66 formed opposite to the anode withan organic EL layer 64 therebetween.

[0012] In addition, the source electrode 50 of the thin film transistorT extends over a second insulating layer 44 and contacts the powerelectrode 42 of the storage capacitor Cst. Also, the anode 58 of theorganic EL diode E extends over the third insulating layer 54 andcontacts the drain electrode of the thin film transistor T.

[0013] FIGS. 3A-3I are sectional views of a method of fabricating theactive matrix type organic EL display panel device of FIG. 2. In FIG.3A, the buffer layer 30 is first formed on an entire surface of theinsulating substrate 1. The buffer layer 30 is formed by depositing afirst insulating material on the substrate 1. Then, the active layer 32a and the capacitor electrode 34 are formed on the buffer layer 30. Theactive layer 32 a and the capacitor electrode 34 are formed bydepositing polycrystalline silicon on the buffer layer 30 and patternedby a first mask process.

[0014] In FIG. 3B, a gate insulating film 36 and the gate electrode 38are formed at a central area of the active layer 32 a. The gateinsulating film 36 and the gate electrode 38 are formed by depositing asecond insulating material and patterned by a second mask process.

[0015] In FIG. 3C, the first insulating layer 40 is formed on the entiresurface of the substrate 1 by depositing a third insulating material.Then, the power electrode 42 is formed on the first insulating layer 40above the capacitor electrode 34.

[0016] In FIG. 3D, the second insulating layer 44 is formed on theentire surface of the substrate 1 by depositing a fourth insulatingmaterial and patterned. The second insulating layer 44 is patterned toform first and second ohmic contact holes 46 a and 46 b exposing regions32 b of the active layer 32 a. The second insulating layer 44 is alsopatterned to expose a portion 48 of the power electrode 42. Then, thesubstrate 1 undergoes an ion doping process, thereby forming source anddrain areas 1 a and 1 b containing impurities.

[0017] In FIG. 3E, the source and drain electrodes 50 and 52 are formedin the first and second ohmic contact holes 46 a and 46 b (shown in FIG.3D) by depositing a third metal material and patterned by a fifth maskprocess. The source electrode 50 extends over the second insulatinglayer 44 and contacts the exposed region 48 (shown in FIG. 3D) of thepower electrode 42.

[0018] In FIG. 3F, the third insulating layer 54 is formed on thesubstrate by depositing a fourth insulating material and patterned by asixth mask process. The third insulating layer 54 is patterned to form adrain contact hole 56 exposing a portion of the drain electrode 52.

[0019] In FIG. 3G, the anode 58 is formed on the substrate 1 bydepositing a transparent conductive material and patterned by a seventhmask process. The anode 58 is on the third insulating layer 54 andcontacts the drain electrode 52 through the drain contact hole 56 (shownin FIG. 3F).

[0020] In FIG. 3H, a protective layer 60 is formed on the substrate 1 bydepositing a fifth insulating material and patterned by an eighty maskprocess. The protective layer exposes a portion 62 of the anode 58. Theprotective layer 60 covers the thin film transistor T and protects thethin film transistor T from moisture and impurities.

[0021] In FIG. 3I, the organic EL layer 64 and the cathode 66 is formedon the substrate 1. In particular, the organic EL layer 64 contacts theexposed portion 62 (shown in FIG. 3H) of the anode 58, and the cathode66 is formed on the entire surface of the substrate 1.

[0022] Accordingly, the organic EL display panel has a lower lightemission scheme where a light emitted in the organic EL layer 64 comesout toward the substrate 1. Accordingly, its light transmittance isdeteriorated because light is transmitted through the first to thirdinsulating layers 40, 44 and 54 and the buffer layer 30. In addition,the organic EL display panel has a reduced light emission efficiency.For example, Formula 1 calculates the light emission efficiency of theorganic EL display panel based on optics principles.

η_(extl)=1/(2n ²)×η_(intl)=1/(2×1.5²)=⅕˜20%   [Formula 1]

[0023] ‘η’ represents internal or external light emission efficiency,and ‘n’ represents the refractive rate of a pertinent substrate. Therefractive rate n of a substrate on which a buffer layer and aninsulating layer are deposited in the related art is 1.5. Thus, in theorganic EL display panel according to the related art, there is adisadvantage in that only 20% of the light emitted from the organic ELlayer 64 to be transmitted through the substrate 1 is utilized on thedisplay panel.

SUMMARY OF THE INVENTION

[0024] Accordingly, the present invention is directed to an activematrix type organic electro luminescence display panel device and amethod of fabricating the same that substantially obviates one or moreof the problems due to limitations and disadvantages of the related art.

[0025] An object of the present invention is to provide an active matrixtype organic electro luminescence display panel device and a method offabricating the same having extended life span and improved lightemission efficiency.

[0026] Another object of the present invention is to provide an activematrix type organic electro luminescence display panel device and amethod of fabricating the same having an organic electro luminescencediode capable of changing the positions of its anode and cathodedepending on the characteristic of carriers applied supplied by the thinfilm transistor, thereby providing uniform brightness.

[0027] Another object of the present invention is to provide an activematrix type organic electro luminescence display panel device and amethod of fabricating the same without employing inorganic insulatingfilms in a light emission region, thereby improving light emissionefficiency and brightness.

[0028] Additional features and advantages of the invention will be setforth in the description which follows, and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

[0029] To achieve these and other advantages and in accordance with thepurpose of the present invention, as embodied and broadly described, theactive matrix organic electro luminescence display panel device includesa substrate, at least one low refractive thin film formed on thesubstrate, and an organic electro luminescence diode formed on the lowrefractive thin film to selectively emit light.

[0030] In another aspect, the method of fabricating an active matrixorganic electro luminescence display panel device includes the steps offorming at least one low refractive thin film on a substrate, andforming an organic electro luminescence diode on the low refractive thinfilm to selectively emit light.

[0031] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory and are intended to provide further explanation of theinvention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciples of the invention. In the drawings:

[0033]FIG. 1 is a diagram of a pixel structure of an active matrix typeorganic EL display panel device according to a related art;

[0034]FIG. 2 is a sectional view of an active matrix type organic ELdisplay panel device according to the related art;

[0035] FIGS. 3A-3I are sectional views of a method of fabricating theactive matrix type organic EL display panel device of FIG. 2;

[0036]FIG. 4 is a sectional view of an exemplary active matrix typeorganic EL display panel device according to the present invention;

[0037] FIGS. 5A-5I are sectional view of an exemplary method offabricating the active matrix type organic EL display panel device ofFIG. 4;

[0038]FIG. 6 is a sectional view of another exemplary active matrix typeorganic EL display panel device according to the present invention;

[0039] FIGS. 7A-7I are section views of an exemplary method offabricating the active matrix type organic EL display panel device ofFIG. 6;

[0040]FIG. 8 is a sectional view of another exemplary active matrix typeorganic EL display panel device according to the present invention; and

[0041] FIGS. 9A-9I are sectional views of an exemplary method offabricating the active matrix type organic EL display panel device ofFIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings.

[0043]FIG. 4 is a sectional view of an exemplary active matrix typeorganic EL display panel device according to the present invention. InFIG. 4, an active matrix type organic EL display panel device may bearranged in a similar manner as shown in FIG. 1 of the related art. Inaddition, the active matrix type organic EL display panel device mayinclude an insulating substrate 1, a low refractive thin film 68 formedon an entire surface of the insulating substrate 1, a buffer layer 70formed on the low refractive thin film 68, a thin film transistor Tformed on a first region of the buffer layer 70, a storage capacitor Cstformed on a second region of the buffer layer 70, and an organic ELdiode E formed on the substrate 1 in a light emitting region I of thelow refractive thin film 68. Further, the storage capacitor Cst and theorganic EL diode E may be electrically connected to the thin filmtransistor T.

[0044] The thin film transistor T may have a deposition structureincluding a semiconductor layer 72 formed on the buffer layer 70, a gateelectrode 78 formed on the semiconductor layer 72, and source and drainelectrodes 90 and 92 formed on the semiconductor layer 72. In addition,the storage capacitor Cst may include a capacitor electrode 74 formed onthe buffer layer 70, and a power electrode 82 formed opposite to thecapacitor electrode 74 with a first insulating layer 80 therebetween.Further, the organic EL diode E may include an anode 98 formed on thelow reflective thin film 68, and a cathode 106 formed opposite to theanode 98 with an organic EL layer 104 therebetween. A protection layer100 also may be formed between a portion of the organic EL layer 104 andthe anode 98. The anode 98 may be formed of a transparent conductivematerial, and the cathode 106 may be formed of a metal having a low workfunction.

[0045] Also, the organic EL layer 104 may include a hole injection layer(not shown), a hole transport layer (not shown), an electron transportlayer (not shown), and an electron injection layer (not shown) formedsequentially between the anode and cathode 98 and 106. If a current isapplied between the anode 98 and the cathode 106, carriers includingelectrons and holes may be injected through the hole injection layer andthe electron injection layer. Such carriers are transported to a lightemission layer (not shown) formed between the hole transport layer andthe electron transport layer through the hole transport layer and theelectron transport layer. At this moment, the hole transport layer andthe electron transport layer transport the carriers to a light emissionmaterial to increase a probability of light emission combination withinthe light emission layer. If the carriers are injected, excitons aregenerated within the light emission layer, and the generated excitonsemit the light corresponding to a polaron energy gap to become extinct.Accordingly, the generated light is radiated toward the insulatingsubstrate 1.

[0046] In addition, the source electrode 90 of the thin film transistorT may extend over a second insulating layer 84, such that a portion ofthe source electrode 90 contacts the power electrode 82 of the storagecapacitor Cst. Also, the anode 98 of the organic EL diode E may extendover a third insulating layer 94, such that a portion of the anode 98contacts the drain electrode 92 of the thin film transistor T. Inparticular, when a gate signal applied by a gate line GL (shown inFIG. 1) of the organic EL display panel device is enabled, the thin filmtransistor may be electrically connected to the storage capacitor Cstand the organic EL diode E. Subsequently, the organic EL diode E mayemit light corresponding to a pixel signal applied by a data line DL(shown in FIG. 1) of the organic EL display panel device. Accordingly,the organic EL display panel device may have a lower light emissionscheme where an emitted light is transmitted through the anode 98, whichis a lower electrode of the organic EL diode E. For example, the anode98 may transmit the emitted light at the organic EL layer 104, thecathode 106 may inject electrons smoothly into the organic EL layer 104because of its low work function.

[0047] Further, the low refractive thin film 68 may be formed of amaterial with low refractive rate, such as silica aerogel or silica gel.In particular, the low refractive thin film 68 may be formed of silicaaerogel with a refractive rate of 1.07. Accordingly, the low refractivethin film 68 may reduce a refraction of light being emitted by theorganic EL diode E. For instance, the display panel device may haveimproved light emission efficiency of about 2.5 times better than thepanel device of the related art as calculated by Formula 2.

η_(extl)=1/(2n ²)×η_(intl)=1/(2×1.07²)˜1/(2×1²)=½=50%   [Formula 2]

[0048] ‘η’ represents internal or external light emission efficiency,and ‘n’ represents the refractive rate of a pertinent substrate.

[0049] Accordingly, in the active matrix type organic EL display paneldevice according to the present invention, light emitted from the lightemission layer of the organic EL layer 104 may be radiated through thesubstrate 1, i.e., be display on a screen of the display pane device,without transmitting through an insulating layer, thereby improvingbrightness and brightness uniformity. Also, light emission is notdispersed, because of its passage through the low refractive thin film68, thereby utilizing more of the screen of the display panel device andimproving light emission efficiency.

[0050] FIGS. 5A-5I are sectional view of an exemplary method offabricating the active matrix type organic EL display panel device ofFIG. 4. In FIG. 5A, the low refractive thin film 68 may be first formedon the entire surface of the insulating substrate 1 by depositing one ofsilica aerogel and silica gel.

[0051] In FIG. 5B, the buffer layer 70 may be formed on a portion of thelow refractive thin film 68. The buffer layer 70 may be formed bydepositing a first insulating material on an entire surface of the lowrefractive thin film 68 and patterned by a first mask process, such thatthe buffed layer 70 is on the substrate 1 except in a portion of thelight emission region I. A mask process may employ a photolithographyincluding coating a photo resist layer, aligning, exposing the photoresist layer and developing. Then, the semiconductor layer 72 and thecapacitor electrode 74 may be formed simultaneously or sequentially bydepositing polycrystalline silicon on an entire surface of the bufferlayer 70 and patterned by a second mask process.

[0052] In FIG. 5C, a gate insulating film 76 and the gate electrode 78may be formed on a central region of the semiconductor layer 72. Thegate insulating layer 76 and the gate electrode 78 may be formed bysequentially depositing a second insulating material and a first metalmaterial on the semiconductor layer 72 and patterned by a third maskprocess, such that the semiconductor layer 72 has two exposed regions 72a and 72 b.

[0053] In FIG. 5D, the first insulating layer 80 may be formed on theentire surface of the substrate 1 covering the low refractive thin film68, the buffer layer 70, the semiconductor layer 72, the gate electrode78, and the capacitor electrode 74. The first insulating layer 80 may beformed by depositing a third insulating material on the entire surfaceof the substrate 1 except in the portion of the light emission region Isimilar to the buffer layer 70. Then, the power electrode 82 may beformed on the first insulating layer 80 above the capacitor electrode74. The power electrode 82 may be formed by depositing a second metalmaterial on the first insulating layer 80 and patterned by a fourth maskprocess.

[0054] In FIG. 5E, the second insulating layer 84 may be formedselectively on the substrate 1 by depositing a third insulating materialon the substrate 1 and patterned by a fifth mask process. In particular,the second insulating layer 84 may be on the entire surface of thesubstrate 1 except in the portion of the light emission region I similarto the buffer layer 70 and the first insulating layer 80. In addition,the first and second insulating layers 80 and 84 may be furtherpatterned to form first and second ohmic contact holes 86 a and 86 bexposing the regions 72 a and 72 b of the semiconductor layer 72.Further, the second insulating layer 84 may be further patterned to forma capacitor contact hole 88 exposing a region of the power electrode 82.Then, the substrate 1 may undergo an ion doping process, thereby formingsource and drain areas Ia and Ib containing impurities.

[0055] In FIG. 5F, the source and drain electrodes 90 and 92 may beformed in the first and second ohmic contact holes 86 a and 86 b (shownin FIG. 5E). The source and drain electrodes 90 and 92 may be formed bydepositing a third metal material and patterned by a sixth mask process,such that the source electrode 90 extends over the second insulatinglayer 84 contacting the exposed region of the power electrode 82 throughthe capacitor contact hole 88 (shown in FIG. 5E). Accordingly, the thinfilm transistor T and the storage capacitor Cst may be completely formedon the substrate 1. In particular, the capacitor electrode 74 mayconnect to the gate electrode 78, and the power electrode 82 may beconnected to a power supply line VDD (shown in FIG. 1) and be parallelto a data line DL (shown in FIG. 1).

[0056] In FIG. 5G, the third insulating layer 94 may be formed on thesubstrate 1 by depositing a fourth insulating material on the entiresurface of the substrate 1 and patterned by a seventh mask process, suchthat the third insulating layer is on the substrate 1 except in theportion of the light emission region I similar to the buffer layer 70,the first insulating layer 80 and the second insulating layer 84. Thethird insulating layer 94 may be further patterned to expose a portionof the drain electrode 92.

[0057] In FIG. 5H, the anode 98 may be formed within the light emissionregion I and on the third insulating layer 94 contacting the exposedportion of the drain electrode 92. The anode 98 may be formed bydepositing a transparent conductive material on the substrate 1 andpatterned by an eighth mask process.

[0058] In FIG. 5I, the protection layer 100 may be formed on thesubstrate 1 by depositing a fifth insulating material on the entiresurface of the substrate 1 and patterned by a ninth mask process. Theprotection layer 100 may be patterned to partially cover the anode 98and to expose a region 102. Also, the protection layer 100 may cover thethin film transistor T, thereby protecting the thin film transistor Tfrom moisture and impurities.

[0059] In FIG. 5J, the organic EL layer 104 and the cathode 106 may besequentially formed on the substrate 1, such that the organic EL layer104 contacts the anode 98 in the region 102 to form the organic EL diodeE.

[0060]FIG. 6 is a sectional view of another exemplary active matrix typeorganic EL display panel device according to the present invention. InFIG. 6, an active matrix type organic EL display panel device mayinclude an insulating substrate 1, a buffer layer 70 formed on theinsulating substrate 1, a thin film transistor T formed on a firstregion of the buffer layer 70, a storage capacitor Cst formed on asecond region of the buffer layer 70, and an organic EL diode E formedon the substrate 1 in a light emitting region I. In particular, thebuffer layer 70 may be formed exposing a region of the substrate 1 inthe light emitting region I, and a third insulating layer 94 and a lowrefractive thin film 68 may be formed on the exposed region of thesubstrate 1, such that the organic EL diode E formed directly on thethird insulating layer 94 and the low refractive thin film 68. The thinfilm transistor T may have a deposition structure including asemiconductor layer 72 formed on the buffer layer 70, a gate electrode78 formed on the semiconductor layer 72, and source and drain electrodes90 and 92 formed on the semiconductor layer 72. In addition the storagecapacitor Cst may include a capacitor electrode 74 formed on the bufferlayer 70, and a power electrode 82 formed opposite to the capacitor 74with a first insulating layer 80 therebetween. Further, the organic ELdiode E may include an anode 98 formed on the low refractive thin film68, a cathode 106 formed opposite to the anode 98 with an organic ELlayer 104 therebetween. Also, the organic EL layer 104 may include ahole injection layer (not shown), a hole transport layer (not shown), anelectron transport layer (not shown), and an electron injection layer(not shown) formed sequentially between the anode and cathode 98 and106. A protection layer 100 also may be formed between a portion of theorganic EL layer 104 and the anode 98.

[0061] In addition, the source electrode 90 of the thin film transistorT may extend over a second insulating layer 84, such that a portion ofthe source electrode 90 contacts the power electrode 82 of the storagecapacitor Cst. Also, the anode 98 of the organic EL diode E may extendover the third insulating layer 94 and the low refractive thin film 68,such that a portion of the anode 98 contacts the drain electrode 92 ofthe thin film transistor T. In particular, when a gate signal applied bya gate line GL (shown in FIG. 1) of the organic EL display panel deviceis enabled, the thin film transistor may be electrically connected tothe storage capacitor Cst and the organic EL diode E. Subsequently, theorganic EL diode E may emit light corresponding to a pixel signalapplied by a data line DL (shown in FIG. 1) of the organic EL displaypanel device. Accordingly, the organic EL display panel device may havea lower light emission scheme where an emitted light is transmittedthrough the anode 98, which is a lower electrode of the organic EL diodeE. For example, the anode 98 may transmit the emitted light at theorganic EL layer 104, the cathode 106 may inject electrons smoothly intothe organic EL layer 104 because of its low work function. Thus, in theactive matrix type organic EL display panel device, light emitted fromthe organic EL layer 104 may be radiated through the substrate 1 withouttransmitting through the buffer layer 70 and the first and secondinsulating layers 80 and 84, thereby improving brightness, brightnessuniformity, and light emission efficiency.

[0062] FIGS. 7A-7I are section views of an exemplary method offabricating the active matrix type organic EL display panel device ofFIG. 6. In FIG. 7A, the buffer layer 70 may be first formed on thesubstrate exposing a portion of the substrate 1 in the light emissionregion I. The buffer layer 70 may be formed by depositing a firstinsulating layer on the entire surface of the substrate 1 and patternedby a first mask process. Then, the semiconductor layer 72 and thecapacitor electrode 74 may be formed simultaneously or sequentially bydepositing polycrystalline silicon on an entire surface of the bufferlayer 70 and patterned by a second mask process.

[0063] In FIG. 7B, a gate insulating film 76 and the gate electrode 78may be formed on a central region of the semiconductor layer 72. Thegate insulating layer 76 and the gate electrode 78 may be formed bysequentially depositing a second insulating material and a first metalmaterial on the semiconductor layer 72 and patterned by a third maskprocess, such that the semiconductor layer has two exposed regions 72 aand 72 b.

[0064] In FIG. 7C, the first insulating layer 80 may be formed on theentire surface of the substrate 1. The first insulating layer 80 may beformed by depositing a third insulating material on the substrate 1.Then, the power electrode 82 may be formed on the first insulating layer80 above the capacitor electrode 74. The power electrode 82 may beformed by depositing a second metal material on the first insulatinglayer 80 and patterned by a fourth mask process.

[0065] In FIG. 7D, the second insulating layer 84 may be formed on thesubstrate 1. A third insulating material may be deposited on the entiresurface of the substrate 1 covering the first insulating layer 80 andthe power electrode 82. Then, the third insulating material and thefirst insulating layer 80 may be patterned to expose the region of thesubstrate 1 in the light emission region I similar to the buffer layer70. Also, the first and second insulating layers 80 and 84 may befurther patterned to form first and second ohmic contact holes 86 a and86 b exposing the regions 72 a and 72 b of the semiconductor layer 72.Further, the second insulating layer 84 may be further patterned to forma capacitor contact hole 88 exposing a region of the power electrode 82.Then, the substrate 1 may undergo an ion doping process, thereby formingsource and drain areas containing impurities in the semiconductor layer72.

[0066] In FIG. 7E, the source and drain electrodes 90 and 92 may beformed in the first and second ohmic contact holes 86 a and 86 b (shownin FIG. 7D). The source and drain electrodes 90 and 92 may be formed bydepositing a third metal material and patterned by a sixth mask process,such that the source electrode 90 extends over the second insulatinglayer 84 and contacts the exposed region of the power electrode 82through the capacitor contact hole 88 (shown in FIG. 7D). Accordingly,the thin film transistor T and the storage capacitor Cst may becompletely formed on the substrate 1. In particular, the capacitorelectrode 74 may connect to the gate electrode 78, and the powerelectrode 82 may be connected to a power supply line VDD (shown inFIG. 1) and be parallel to a data line DL (shown in FIG. 1).

[0067] In FIG. 7F, the third insulating layer 94 may be formed on theentire surface of the substrate 1 by depositing a fourth insulatingmaterial on the entire surface of the substrate 1. Then, the lowrefractive thin film 68 may be formed on an entire surface of the thirdinsulating layer 94 by depositing one of silica aerogel and silica gel.Then, the third insulating layer 94 and the low refractive thin film 68may be patterned by a seventh mask process to form a drain contact holeexposing a portion of the drain electrode 92.

[0068] In FIG. 7G, the anode 98 may be formed within the light emissionregion I and on the low refractive thin film 68 contacting the exposedportion of the drain electrode 92. The anode 98 may be formed bydepositing a transparent conductive material on the substrate 1 andpatterned by an eighth mask process.

[0069] In FIG. 7H, the protection layer 100 may be formed on thesubstrate 1 by depositing a fifth insulating material on the entiresurface of the substrate an patterned by a ninth mask process. Theprotection layer 100 may be patterned to partially cover the anode 98and to expose a region 102. Also, the protection layer 100 may cover thethin film transistor T, thereby protecting the thin film transistor Tfrom moisture and impurities.

[0070] In FIG. 7I, the organic EL layer 104 and the cathode 106 may besequentially formed on the substrate 1, such that the organic EL layer104 contacts the anode 98 in the region 102 to form the organic EL diodeE.

[0071]FIG. 8 is a sectional view of another exemplary active matrix typeorganic EL display panel device according to the present invention. InFIG. 8, an active matrix type organic EL display panel device may bearranged in a similar manner as shown in FIG. 1. In addition, the activematrix type organic EL display panel device may include an insulatingsubstrate 1, a low refractive thin film 108 formed on an entire surfaceof the substrate 1, a buffer layer 70 formed on the low refractive thinfilm 108, a thin film transistor T formed on a first region of thebuffer layer 70, a storage capacitor Cst formed on a second region ofthe buffer layer 70, and organic EL diode E formed on the substrate 1 ina light emitting region I.

[0072] The thin film transistor T may have a deposition structureincluding a semiconductor layer 72 formed on the buffer layer 70, a gateelectrode 78 formed on the semiconductor layer 72, and source and drainelectrodes 90 and 92 formed on the semiconductor layer 72. In addition,the storage capacitor Cst may include a capacitor electrode 74 formed onthe buffer layer 70, and a power electrode 82 formed opposite to thecapacitor electrode 74 with a first insulating layer 80 therebetween.Further, the organic EL diode E may include an anode 98 formed on thelow reflective thin film 68, the first insulating layer 80, a secondinsulating layer 84 and a third insulating layer 98. The organic ELdiode E may also include a cathode 106 formed opposite to the anode 98with an organic EL layer 104 therebetween. Also, the organic EL layer104 may include a hole injection layer (not shown), a hole transportlayer (not shown), an electron transport layer (not shown), and anelectron injection layer (not shown) formed sequentially between theanode and cathode 98 and 106. A protection layer 100 also may be formedbetween a portion of the organic EL layer 104 and the anode 98. Theanode 98 may be formed of a transparent conductive material, and thecathode 106 may be formed of a metal having a low work function.

[0073] In addition, the source electrode 90 of the thin film transistorT may extend over the second insulating layer 84, such that a portion ofthe source electrode 90 contacts the power electrode 82 of the storagecapacitor Cst. Also, the anode 98 of the organic EL diode E may extendover the third insulating layer 94, such that a portion of the anode 98contacts the drain electrode 92 of the thin film transistor T. Inparticular, when a gate signal applied by a gate line GL (shown inFIG. 1) of the organic EL display panel device is enabled, the thin filmtransistor may be electrically connected to the storage capacitor Cstand the organic EL diode E. Subsequently, the organic EL diode E mayemit light corresponding to a pixel signal applied by a data line DL(shown in FIG. 1) of the organic EL display panel device. Accordingly,the organic EL display panel device may have a lower light emissionscheme where an emitted light is transmitted through the anode 98, whichis a lower electrode of the organic EL diode E. For example, the anode98 may transmit the emitted light at the organic EL layer 104, thecathode 106 may inject electrons smoothly into the organic EL layer 104because of its low work function.

[0074] Accordingly, in the active matrix type organic EL display paneldevice according to the present invention, light emitted from the lightemission layer of the organic EL layer 104 may be radiated through thelow refractive thin film 108 and the substrate 1, thereby improvingbrightness and brightness uniformity.

[0075] FIGS. 9A-9I are sectional views of an exemplary method offabricating the active matrix type organic EL display panel device ofFIG. 8. In FIG. 9A, the low refractive thin film 108 may be first formedon the entire surface of the insulating substrate 1 by depositing one ofsilica aerogel and silica gel.

[0076] In FIG. 9B, the buffer layer 70 may be formed on a portion of thelow refractive thin film 108. The buffer layer 70 may be formed bydepositing a first insulating material on an entire surface of the lowrefractive thin film 108. Then, the semiconductor layer 72 and thecapacitor electrode 74 may be formed simultaneously or sequentially bydepositing polycrystalline silicon on an entire surface of the bufferlayer 70 and patterned by a first mask process.

[0077] In FIG. 9C, a gate insulating film 76 and the gate electrode 78may be formed on a central region of the semiconductor layer 72. Thegate insulating layer 76 and the gate electrode 78 may be formed bysequentially depositing a second insulating material and a first metalmaterial on the semiconductor layer 72 and patterned by a second maskprocess, such that the semiconductor layer 72 has two exposed regions atits ends.

[0078] In FIG. 9D, the first insulating layer 80 may be formed on theentire surface of the substrate 1. The first insulating layer 80 may beformed by depositing a third insulating material on the entire surfaceof the substrate 1. Then, the power electrode 82 may be formed on thefirst insulating layer 80 above the capacitor electrode 74. The powerelectrode 82 may be formed by depositing a second metal material on thefirst insulating layer 80 and patterned by a third mask process.

[0079] In FIG. 9E, the second insulating layer 84 may be formed on thesubstrate 1 by depositing a third insulating material on the substrate 1and patterned by a fourth mask process. In particular, the secondinsulating layer 84 may be on the entire surface of the substrate 1. Inaddition, the first and second insulating layers 80 and 84 may bepatterned to form first and second ohmic contact holes 86 a and 86 bexposing the regions 72 a and 72 b of the semiconductor layer 72.Further, the second insulating layer 84 may be further patterned to forma capacitor contact hole 88 exposing a region of the power electrode 82.Then, the substrate 1 may undergo an ion doping process, thereby formingsource and drain areas Ia and Ib containing impurities.

[0080] In FIG. 9F, the source and drain electrodes 90 and 92 may beformed in the first and second ohmic contact holes 86 a and 86 b (shownin FIG. 5E). The source and drain electrodes 90 and 92 may be formed bydepositing a third metal material and patterned by a fifth mask process,such that the source electrode 90 extends over the second insulatinglayer 84 contacting the exposed region of the power electrode 82 throughthe capacitor contact hole 88 (shown in FIG. 5E). Accordingly, the thinfilm transistor T and the storage capacitor Cst may be completely formedon the substrate 1. In particular, the capacitor electrode 74 mayconnect to the gate electrode 78, and the power electrode 82 may beconnected to a power supply line VDD (shown in FIG. 1) and be parallelto a data line DL (shown in FIG. 1).

[0081] In FIG. 9G, the third insulating layer 94 may be formed on thesubstrate 1 by depositing a fourth insulating material on the entiresurface of the substrate 1 and patterned by a sixth mask process. Thethird insulating layer 94 may be patterned to expose a portion 96 of thedrain electrode 92.

[0082] In FIG. 9H, the anode 98 may be formed within the light emissionregion I and on the third insulating layer 94 contacting the exposedportion 96 (shown in FIG. 9G) of the drain electrode 92. The anode 98may be formed by depositing a transparent conductive material on thesubstrate 1 and patterned by a seventh mask process.

[0083] In FIG. 9I, the protection layer 100 may be formed on thesubstrate 1 by depositing a fifth insulating material on the entiresurface of the substrate 1 and patterned by an eighth mask process. Theprotection layer 100 may be patterned to partially cover the anode 98and to expose a region 102. Also, the protection layer 100 may cover thethin film transistor T, thereby protecting the thin film transistor Tfrom moisture and impurities.

[0084] In FIG. 9J, the organic EL layer 104 and the cathode 106 may besequentially formed on the substrate 1, such that the organic EL layer104 contacts the anode 98 in the region 102 to form the organic EL diodeE.

[0085] It will be apparent to those skilled in the art that variousmodifications and variations can be made in the active matrix typeorganic electro luminescence display panel device and the method offabricating the same of the present invention without departing from thespirit or scope of the invention. Thus, it is intended that the presentinvention cover the modifications and variations of this inventionprovided they come within the scope of the appended claims and theirequivalents.

What is claimed is:
 1. An active matrix organic electro luminescencedisplay panel device, comprising: a substrate; at least one lowrefractive thin film formed on the substrate; and an organic electroluminescence diode formed on the low refractive thin film to selectivelyemit light.
 2. The device according to claim 1, wherein a refractiverate (n) of the low refractive thin film is less than or equal to 1.5.3. The device according to claim 2, wherein the low refractive thin filmincludes at least one of silica aerogel and silica gel.
 4. The deviceaccording to claim 1, further comprising: a switching device formed onthe low refractive thin film for selectively driving the organic electroluminescence diode; and a capacitor for sustaining a light emission ofthe organic electro luminescence diode.
 5. The device according to claim4, wherein the organic electro luminescence diode includes: a firstelectrode formed of transparent conductive material on the lowrefractive thin film and connected to the switching device; an organiclight emission layer including an organic luminous material on the firstelectrode; and a second electrode including a metal material to coverthe organic light emission layer, the switching device, and thecapacitor.
 6. The device according to claim 5, wherein the switchingdevice includes: a buffer layer formed on the substrate; a semiconductorlayer formed at a predetermined area on the buffer layer; a gateinsulating film and a gate electrode sequentially deposited on thesemiconductor layer; a drain electrode connected to the semiconductorlayer and connected to the first electrode of the organic electroluminescence diode; and a source electrode connected to thesemiconductor layer and connected to the capacitor.
 7. The deviceaccording to claim 6, wherein the capacitor includes: a capacitorelectrode formed on the buffer layer and separated from thesemiconductor layer with a gap therebetween; a first insulating layercovering the capacitor electrode; and a power electrode overlapping thecapacitor electrode on the first insulating layer and connected to thesource electrode.
 8. The device according to claim 6, furthercomprising: a second insulating layer covering the switching device andthe capacitor, wherein the second insulating layer includes a contacthole and a portion of the first electrode is within the contact hole;and a third insulating layer formed between the second insulating layerand the second electrode.
 9. The device according to claim 5, furthercomprising at least one fourth insulating layer formed between the lowrefractive thin film and the first electrode.
 10. The device accordingto claim 1, further comprising: a switching device formed between thesubstrate and the low refractive thin film; and a capacitor formedbetween the substrate and the low refractive thin film to sustain alight emission of the organic electro luminescence diode.
 11. The deviceaccording to claim 10, wherein the organic electro luminescence diodeincludes: a first electrode formed of transparent conductive material onthe low refractive thin film, wherein the low refractive thin filmincludes a contact hole and a portion of the first electrode is withinthe contact hole contacting the switching device; an organic lightemission layer formed of organic luminous material on the firstelectrode; and a second electrode formed of metal material to cover theorganic light emission layer, the switching device and the capacitor.12. The device according to claim 11, wherein the switching deviceincludes: a buffer layer formed on the substrate; a semiconductor layerformed at a predetermined area on the buffer layer; a gate insulatingfilm and a gate electrode sequentially deposited on the semiconductorlayer; a drain electrode connected to the semiconductor layer andconnected to the first electrode of the organic electro luminescencediode; and a source electrode connected to the semiconductor layer andconnected to the capacitor.
 13. The device according to claim 12,wherein the capacitor includes: a capacitor electrode formed on thebuffer layer and separated from the semiconductor layer with a gaptherebetween; a first insulating layer covering the capacitor electrode;and a power electrode overlapping the capacitor electrode on the firstinsulating layer and connected to the source electrode.
 14. The deviceaccording to claim 12, further comprising a second insulating layerformed between the substrate and the low refractive thin film to coverthe switching device and the capacitor.
 15. A method of fabricating anactive matrix organic electro luminescence display panel device,comprising the steps of: forming at least one low refractive thin filmon a substrate; and forming an organic electro luminescence diode on thelow refractive thin film to selectively emit light.
 16. The methodaccording to claim 15, further comprising the step of: forming aswitching device and a capacitor on the low refractive thin film,wherein the switching device is provided for driving the organic electroluminescence diode and the capacitor is provided for sustaining thelight emission of the organic electro luminescence diode.
 17. The methodaccording to claim 15, wherein a refractive rate (n) of the lowrefractive thin film is less than or equal to 1.5.
 18. The methodaccording to claim 15, wherein the low refractive thin film includes atleast one of silica aerogel and silica gel.
 19. The method according toclaim 16, wherein the step of forming the organic electro luminescencediode includes: forming a first electrode of transparent conductivematerial on the low refractive thin film connected with the switchingdevice; forming an organic light emission layer of organic luminousmaterial on the first electrode; and forming a second electrode of metalmaterial to cover the organic light emission layer, the switchingdevice, and the capacitor.
 20. The method according to claim 19, whereinthe step of forming the switching device includes: forming a bufferlayer on the substrate; forming a semiconductor layer at a predeterminedarea on the buffer layer; forming a gate insulating film and a gateelectrode sequentially on the semiconductor layer; forming a drainelectrode connected to the semiconductor layer and connected to thefirst electrode of the organic electro luminescence diode; and forming asource electrode connected to the semiconductor layer and connected tothe capacitor at the same time when forming the drain electrode.
 21. Themethod according to claim 20, wherein the step of forming the capacitorincludes: forming a capacitor electrode on the buffer layer to beseparated from the semiconductor layer with a gap therebetween; forminga first insulating layer to cover the capacitor electrode; and forming apower electrode overlapping the capacitor electrode on the firstinsulating layer and connected to the source electrode.
 22. The methodaccording to claim 19, further comprising the steps of: forming a secondinsulating layer to cover the switching device and the capacitor,wherein the second insulating layer includes a contact hole and aportion of the first electrode is within the contact hole; and forming athird insulating layer formed between the second insulating layer andthe second electrode.
 23. The method according to claim 19, furthercomprising the step of forming at least one fourth insulating layerformed between the low refractive thin film and the first electrode. 24.The method according to claim 15, further comprising the step of:forming a switching device between the substrate and the low refractivethin film; and forming a capacitor between the substrate and the lowrefractive thin film for sustaining the light emission of the organicelectro luminescence diode.
 25. The method according to claim 24,wherein the step of forming the organic electro luminescence diodeincludes: forming a first electrode of transparent conductive materialon the low refractive thin film, wherein the low refractive thin filmincludes a contact hole and a portion of the first electrode is withinthe contact hole contacting the switching device; forming an organiclight emission layer of organic luminous material on the firstelectrode; and forming a second electrode of metal material to cover theorganic light emission layer, the switching device and the capacitor.26. The method according to claim 25, wherein the step of forming theswitching device includes: forming a buffer layer on the substrate;forming a semiconductor layer at a predetermined area on the bufferlayer; forming a gate insulating film and a gate electrode sequentiallyon the semiconductor layer; forming a drain electrode connected to thesemiconductor layer and connected to the first electrode of the organicelectro luminescence diode; and forming a source electrode connected tothe semiconductor layer and connected to the capacitor at the same timewhen forming the drain electrode.
 27. The method according to claim 26,wherein the step of forming the capacitor includes: forming a capacitorelectrode on the buffer layer to be separated from the semiconductorlayer with a specific gap therebetween; forming a first insulating layerto cover the capacitor electrode; and forming a power electrode tooverlap the capacitor electrode on the first insulating layer andconnected to the source electrode.
 28. The method according to claim 26,further comprising the step of forming a second insulating layer betweenthe substrate and the low refractive thin film to cover the switchingdevice and the capacitor.